stands, had been one of the deep parts of the basin in which the 

 London clay was being deposited. The two wells, however (that 

 of Trafalgar Square and that of the Society), correspond in 

 one point which is of excessively rare occurrence, wholly beyond 

 provision, and a pure matter of chance : out of numerous wells 

 bored by Messrs. Easton, Amos, & Sons, for instance, these two 

 are the only instances in whieh it has occurred. Whilst boring 

 through the chalk, in both cases, the instrument came upon a 

 fissure and dropped down a space of several feet. To understand 

 the significance of this, it is necessary to remember that the 

 manner in which the water in the chalk finds its way to the 

 surface, or into the sea, is through such fissures. An example of 

 its issuing at the surface from them may be seen in the river 

 Wandle, which takes its rise at Carshalton, near Croydon, pouring 

 out through such fissures a river ready made. An instance of 

 its falling into the sea out of such fissures may be seen at low 

 water near Brighton, where a succession of vertical fissures, from 

 the narrowest chink to 6 inches wide, occurring at varying dis- 

 tances from each other, pours out an immense quantity of fresh 

 water. Such fissures act as the main channels by which the 

 water in the chalk finds its way to the sea. When a well sunk 

 into the chalk does not fall upon one of these, it is dependent 

 for water on what may percolate through the surrounding chalk 

 into the well ; but if it light upon a fissure, its sujjply is drawn 

 from a stream itself, and of course will depend upon the size 

 of the stream how far it may be exhaustible. The quantity of 

 water percolating through the chalk, however', is so great, that 

 for aU ordinary purj)ose.s, any well sunk for some depth in it is 

 sufficient, if a very large supply is not wanted; the only draw- 



